1. Field of the Invention
The present invention relates to a system for feeding the power to a telephone terminal/terminals connected to a LAN (Local Area Network).
2. Description of the Related Art
In recent years, the so-called downsizing has been rapidly developed in the information processing field. For facilitating the downsizing, technology of LAN""s has been developed for achieving distributed processing or horizontal distributed processing using a plurality of work stations or personal computers. Simultaneously, technology of LAN telephone terminals adapted for the LAN environment has also been developed. In this case, it is important to realize a power feeding system for the LAN telephone terminals.
Specifically, in transmission lines forming the LAN environment, data signals are flowing. Thus, it is difficult to use those transmission lines as power feed lines as in the public network. In particular, this is almost impossible in Ethernet LAN""s wherein Manchester codes having no DC components are used as transmission codes. As is known in the art, the Manchester code is a code whose polarity is inverted at the center of a bit sequence so as to define a logical value of 1 or 0 by a direction of the inversion. Under the circumstances, the telephone terminals in the LAN receive the power from the commercial power source via AC adapters, respectively.
In this technique, however, since the respective telephone terminals receive the power from the commercial power source via the AC adapters, installation of the telephone terminals is troublesome. Further, every time an installed position of the telephone terminal is changed, an operator is required to make the installed position thereof clear relative to the network, thereby lacking in portability.
Therefore, it is an object of the present invention to provide a power feeding system in a LAN which is simple in structure while being capable of automatically judging whether a connected terminal is a telephone terminal or a terminal other than the telephone terminal, so as to automatically feed the power to the telephone terminal.
According to one aspect of the present invention, there is provided, in a LAN having terminals connected to each other via cables extending from a line concentrator, each of the cables including therein a signal line for delivering data signals for mutual communication between the terminals and the terminals including at least one telephone terminal, a power feeding system comprising a power feed line included in each of the cables; a power feed section for feeding power to the at least one telephone terminal via the corresponding power feed line; power feed control switching sections each for establishing or disabling communication between the power feed section and the corresponding power feed line; a current monitor section for detecting whether a value of current flowing in each of the power feed lines when each of the power feed lines is connected to the power feed section is within a preset current value range which represents a state where the telephone terminal is connected to the cable including therein the corresponding power feed line; and a control section for controlling the power feed control switching sections to connect the corresponding power feed lines to the power feed section in sequence, and for controlling each of the power feed control switching sections to stop feeding the power via the corresponding power feed line when the current monitor section detects that the value of the current flowing in the corresponding power feed line is outside the preset current value range, and to continue feeding the power via the corresponding power feed line when the current monitor section detects that the value of the current flowing in the corresponding power feed line is within the preset current value range.
It may be arranged that the power feeding system further comprises a link detecting section for monitoring each of the signal lines in sequence to detect whether link of the terminal connected to the corresponding signal line is established, wherein the control section controls the corresponding power feed control switching section to continue feeding the power to the corresponding power feed line when the link detecting section detects that the link of the terminal connected to the corresponding signal line is established, while the value of the current flowing in the corresponding power feed line is detected to be within the preset current value range.
It may be arranged that the power feeding system further comprises a link detecting section for monitoring each of the signal lines in sequence to detect whether link of the terminal connected to the corresponding signal line is established, wherein the control section controls the corresponding power feed control switching section to continue to stop feeding the power to the corresponding power feed line when the link detecting section detects that the link of the terminal connected to the corresponding signal line is established, while the corresponding power feed line is disconnected from the power feed section by the corresponding power feed control switching section.
It may be arranged that the power feeding system further comprises a line state monitor table for storing given states of the power feed line and the signal line of each of the cables, wherein the control section controls, by switching among the cables per given period, an operation of the whole power feeding system including the operations of the power feed control switching sections based on the line state monitor table.